When video is shot under an environment illuminated with a (non-inverter) fluorescent lamp, the luminance signal varies due to the AC voltage frequency of the fluorescent lamp (at 50 Hz or 60 Hz), thus producing bright and dark portions in an image shot. Such a phenomenon is generally called “flicker”. In the field of such a flicker reducing technique, the technique disclosed in Patent Document No. 1 is known, for example.
The image capture device disclosed in Patent Document No. 1 stores, in a memory, as many line integral values as the number of frames corresponding to the greatest common divisor of the flicker period and frame period. In this case, each of the line integral values is obtained by calculating the integral of pixel values on a horizontal line basis within a frame. Among multiple frames, the line integral values are normalized based on the average of the line integral values of associated horizontal lines. And based on that normalized line integral value, flicker is analyzed.
FIG. 6 illustrates a configuration for a main part of a flicker reducing section (which is also called “flicker reducing means”) provided for a conventional image capture device. The configuration of the flicker reducing section of the image capture device disclosed in Patent Document No. 1 can be described with reference to FIG. 6.
In FIG. 6, a line integration section 11 receives image signals which have been input to this flicker reducing section 11 and calculates a line integral value of the image signals for a single horizontal line on a line-by-line basis. A sampling section 12 extracts a line integral value associated with a predetermined line from the line integral values supplied from the line integration section 11. A line integral value memory 13 stores the line integral value that has been extracted by the sampling section 12 for a predetermined number of frames (or fields). In the following description, the line integral value memory 13 is supposed to store the line integral value for a predetermined number of frames.
A difference calculating section 51 calculates the difference (i.e., an inter-frame difference) between a first line integral value supplied from the sampling section 12 and a second line integral value retrieved from the line integral value memory 13. In this case, the “second line integral value” refers herein to the line integral value of a horizontal line, which is located at the same coordinates as a horizontal line where the first line integral value has been obtained, within the previous frame that is stored in the line integral value memory 13.
An average value calculating section 52 calculates the average value of the line integral values based on the first line integral value and the line integral values of multiple frames which have been obtained earlier than the latest one from a horizontal line that is located at the same coordinates as the horizontal line where the first line integral value has been obtained. A normalizing section 53 divides the inter-frame difference obtained by the difference calculating section 51 by the average line integral value obtained by the average value calculating section 52, thereby calculating a normalized difference value in which the inter-frame difference has been normalized.
An interline DFT (discrete Fourier transform) section 54 performs a discrete Fourier transform on the normalized differential value that has been obtained by the normalizing section 53. A flicker coefficient section 17 determines the amplitudes and phases of respective degrees of flicker components based on the Fourier transform coefficient obtained by the interline DFT section 54. And based on those amplitudes and phases, the flicker coefficient section 17 generates a flicker coefficient associated with the pixel value which is currently input to this flicker reducing section. Based on the flicker coefficient that has been generated by the flicker coefficient section 17, a correction arithmetic section 18 corrects the input image entered into this flicker reducing section 1. Specifically, the correction arithmetic section 18 removes flicker by dividing the input pixel value by the flicker coefficient plus one.